1. Field of the Invention
The present invention relates to elastic wave devices, such as elastic boundary wave devices and surface acoustic wave devices, and in particular, relates to elastic wave devices including first wiring portions that are electrically connected to IDT electrodes and that are electrically connected to second wiring portions disposed on insulating films.
2. Description of the Related Art
Surface acoustic wave devices and elastic boundary wave devices have been used for, for example, band-pass filters of cellular phones. In order to reduce the size of electronic devices, these elastic boundary wave devices need to be mountable on circuit boards by flip-chip bonding using metal bumps.
For example, Japanese Unexamined Patent Application Publication No. 2007-28195 discloses an elastic boundary wave device including solder bumps mountable on circuit boards by flip-chip bonding. FIG. 12 is a fragmentary sectional view of the elastic boundary wave device described in Japanese Unexamined Patent Application Publication No. 2007-28195. An elastic boundary wave device 1001 includes a piezoelectric substrate 1002. A dielectric layer 1003 is laminated on the piezoelectric substrate 1002. An electrode 1004 including an IDT electrode is disposed between the piezoelectric substrate 1002 and the dielectric layer 1003. Although the IDT electrode is not illustrated, an electrode pad 1004a that is electrically connected to the IDT electrode is illustrated.
Moreover, a sound absorbing film 1005 arranged to absorb leaking elastic waves or bulk waves is laminated on the upper surface of the dielectric layer 1003.
A first wiring portion 1006 is provided on the piezoelectric substrate 1002 so as to be electrically connected to the electrode pad 1004a. The dielectric layer 1003 includes a through-hole 1003a, and the first wiring portion 1006 is partially exposed through the through-hole 1003a. Furthermore, a second wiring portion 1007 is provided on the dielectric layer 1003. A portion 1007a of the second wiring portion 1007 extends into the through-hole 1003a, and the second wiring portion 1007 is electrically connected to the first wiring portion 1006. Moreover, a through-hole 1005a is provided in the sound absorbing film 1005 so as to communicate with the through-hole 1003a. An under-bump metal layer 1008 is disposed in an opening defined by the through-holes 1003a and 1005a, and a solder bump 1009 is disposed on the under-bump metal layer 1008. This solder bump 1009 is connected to an electrode land on a circuit board.
The second wiring portion 1007 is also electrically connected to, for example, other first wiring portions provided on other portions of the elastic boundary wave device 1001. Therefore, the second wiring portion 1007 is routed on the upper surface of the dielectric layer 1003 so as to electrically connect a plurality of portions.
On the other hand, a reduction in size of the elastic boundary wave device 1001 has been highly desirable. Accordingly, the second wiring portion 1007 is routed so as to electrically connect portions to be connected to each other with the shortest possible length. Therefore, IDT electrodes, for example, are arranged under the second wiring portion 1007 at some locations.
The elastic boundary wave device 1001 described in Japanese Unexamined Patent Application Publication No. 2007-28195 can be reduced in size since the second wiring portion 1007 is routed so as to electrically connect the portions to be connected to each other with the shortest possible length. However, the device disadvantageously has poor electrical characteristics, for example, low filter characteristics, since relatively intense high-frequency spurious components caused by unwanted waves such as bulk waves occur in the device.